This invention relates to an improved duplex latch-bolt mechanism having an adjustable cam device and a displacement jacket assembly adapted to enable the latch-bolt mechanism to be conveniently adjusted for any door fitting arrangement.
Traditionally, latch-bolt mechanisms used in known cylinder door locks are usually confined to two kinds of backset configurations--namely, a 60 mm type and a 70 mm type backset configurations. As ordinary consumers, however, are unaware of this situation, a great deal of inconvenience has been caused in the installation of door locks either by the need to change to another type of door lock or by the need to make mechanical modifications to the latch-bolt mechanism of the unsuitable door lock. In consideration of this problem, studies and improvements have been made to provide a duplex latch-bolt mechanism adapted to both the 60 mm and 70 mm backset configurations. Typical products of this latch-bolt mechanism are generally classified into the following two types:
1) A fixed duplex latch-bolt mechanism in whichthe length of the latch-bolt mechanism 1, as shown in FIG. 1(A), is fixed for a 60 mm as well as for a 70 mm door fitting arrangement. Although this kind of latch-bolt mechanism can be adaptable to a door lock arrangement without requiring a mechanical modification of the latch bolt itself, problems still exist. As shown in FIG. 1(B), when the door lock arrangement 8 (i.e. the installation distance provided from the door post edge 6 to the central point of the lock opening 7 in the door), is made for installing a 60 mm type latch-bolt mechanism, the length of the latch-bolt mechanism 1 will exceed a distance 9 of the lock opening 7. Consequently, the door lock opening 7 in the door has to be re-drilled to a greater depth 10 so as to accommodate the entire length of the fixed duplex latch-bolt mechanism 1, causing a certain inconvenience in the installation process.
2.) An adjustable duplex latch-bolt mechanism in which the length of the latch bolt mechanism 2, as shown in FIG. 2, is fixed for a 60 mm door fitting arrangement, and depending on the requirements of the installation conditions, an adjustment from the latch-bolt mechanism can be made to adapt to a 70 mm door fitting arrangement. Although this kind of latch-bolt mechanism has overcome the shortcoming suffered by the fixed duplex latch-bolt mechanism as mentioned in 1), above, difficulty often occurs in making said adjustment. As can be seen in FIG. 2, when making an adjustment to the latch-bolt mechanism 1', a shifting sleeve 3 has to be pulled out to re-align the positioning openings 31 with the transfer openings 111, 51 (41), and 121 in said latch-bolt mechanism 1'. Since no positioning fittings are provided on the shifting sleeve 3, it is not only inconvenient for the user to hold the shifting sleeve 3 in position, but said sleeve 3 also frequently comes off during the removal operation. In addition, to dispose the two transfer gears 4, 5 in the limited space of the latch-bolt mechanism 1' also introduces some difficulty to the manufacturing process.
In addition, a known dual backset latch was disclosed in Taiwan under Patent Publication No. 82244 on Nov. 1, 1986, which corresponds to U.S. application No. 639,715 filed Aug. 4, 1984 now U.S. Pat. No. 4,615,549. The problems of the disclosed invention are as follows:
1) The entire structure of this backset latch is designed to adapt to a special latch-handle assembly wherein cylindrical support nuts as normally provided in the known art are not used. Therefore, this backset latch requires a specific latch-handle assembly, a requirement which is both inefficient and uneconomic.
2) Since the front and rear cams of the backset latch are both C-shaped, the unlocking operation of the backset latch is always undertaken by the three sides of said cams, resulting in considerable unstability and wear thereof.
In order to solve the problems suffered by the prior art, the applicant has specifically designed a duplex latch-bolt mechanism which can be adapted to any door fitting arrangement by a mere adjustment, the application for which was filed on Jan. 7, 1986 in the U.S. under Ser. No. 817,422, and the patent for which was granted on Dec. 8, 1987 under U.S. Pat. No. 4,711,477. However, since the above-mentioned patent was designed for those cylinder door locks adaptable only to a unique curved transfer member, efforts were made to develop another novel structure for cylinder door locks with a square transfer member.